1. Field of the Invention
The present invention relates to a process and apparatus for producing molten metal (which term includes metal alloys), in particular although by no means exclusively iron, from metalliferous feed material, such as ores, partly reduced ores and metal-containing waste streams, in a metallurgical vessel containing a molten bath.
The present invention relates particularly to a molten metal bath-based direct smelting process and apparatus for producing molten metal from a metalliferous feed material.
2. Description of Related Arts
The most widely used process for producing molten iron is based on the use of a blast furnace. Solid material is charged into the top of the furnace and molten iron is tapped from the hearth. The solid material includes iron ore (in sinter, lump or pellet form), coke, and fluxes and forms a permeable burden that moves downwardly. Preheated air, which may be oxygen enriched, is injected into the bottom of the furnace and moves upwardly through the permeable bed and generates carbon monoxide and heat by combustion of coke. The result of these reactions is to produce molten iron and slag.
A process that produces iron by reduction of iron ore below the melting point of the iron produced is generally classified as a xe2x80x9cdirect reduction processxe2x80x9d and the product is referred to as DRI.
The FIOR (Fluid Iron Ore Reduction) process is an example of direct reduction process. The process reduces iron ore fines as the fines are gravity-fed through each reactor in a series of fluid bed reactors. The fines are reduced in solid state by compressed reducing gas that enters the bottom of the lowest reactor in the series and flows counter-current to the downward movement of fines.
Other direct reduction processes include moving shaft furnace-based processes, static shaft furnace-based processes, rotary hearth-based processes, rotary kiln-based processes, and retort-based processes.
The COREK process includes a direct reduction process as one stage. The COREX process produces molten iron directly from coal without the large requirements for coal, as a blast furnace. The COREX process includes 2-stage operation in which:
(a) DRI is produced in a shaft furnace from a permeable bed of iron ore (in lump or pellet form), coal and flexes; and
(b) the DRI is then charged without cooling into a connected meltor gasifier and melted.
Partial combustion of coal in the melter gasifier produces reducing gas for the shaft furnace.
Another known group of processes for producing iron is based on cyclone converters in which iron ore is melted by combustion of oxygen and reducing gas in an upper melting cyclone and is smelted in a lower smelter generates the reducing gas for the upper melting cyclone.
A process that produces molten metal directly from ores (and partially reduced ores) is generally referred to as a xe2x80x9cdirect smelting processxe2x80x9d.
One known group of direct smelting processes is based on the use of electric furnaces as the major source of energy for the smelting reactions.
Another known direct smelting process, which is generally referred to as the Romelt process, is described in Australian patent 604237 in the name of Moskovsky Institut Statis Splavov. The Romelt process is based on the use of a large volume, highly agitated slag bath as the medium for smelting top-charged metal oxides to metal and for post-combusting gaseous reaction products and transferring the heat as required in continue smelting metal oxides. The Romelt process includes injection of oxygen enriched air or oxygen into the size via a lower row of tuyeres to provide slag agitation and injection of oxygen intothe also via an upper row of tuyeres to promote post-combustion. The slag volume above the lower row of tuyeres forms an xe2x80x9cupper bubbling zonexe2x80x9d and the slag volume below the lower row of tuyeres forms a xe2x80x9cquiescent slag melt zonexe2x80x9d. The upper bubbling zone is the main reaction medium, and molten metal droplets that form in this slag volume move downwardly by gravity through the quiescent slag melt zone and collect in a metal layer. In the Romelt process the metal layer is not an important reaction medium.
Another known group of direct smelting process that are slag-based is generally described as xe2x80x9cdeep slagxe2x80x9d processes. These processes, such as DIOS and AISI processes, are based on forming a deep layer of foaming slag. As with the Romelt process, the metal layer below the slag layer is not an important reaction medium.
Another known direct smelting process which relies on a molten metal layer as a reaction medium, and is generally referred to as the HIsmelt process, is described in International application PCT/AU96/00197 (WO 96/31627) in the name of the applicant.
The HIsmelt process as described in the International application comprises:
(a) forming a bath of molten iron and slag in a vessel;
(b) injection into the bath;
(i) a metalliferous feed material, typically metal oxides; and
(ii) a solid carbonaceous material, typically coal, which acts as a reductant of the metal oxides and a source of energy; and
(c) smelting the metalliferous feed material to metal in the metal layer.
The HIsmelt process also comprises post-combusting reaction gases, such as CO and H1, released from the bath in the space above the bath with oxygen-containing gas and transferring the heat generated by the post-combustion to the bath to contribute to the thermal energy required to smelt the metalliferous feed materials.
The HIsmelt process also comprises forming a transition zone above the nominal quiescent surface of the bath in which there are ascending and thereafter descending droplets or splashes or streams of molten metal and/or slag which provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath.
The applicant has carried out extensive pilot plant work on the HIsmelt process and has made a series of significant findings in relation to the process.
In general terms, the present invention is a direct smelting process for producing metals from metalliferous feed material which includes the steps of:
(a) forming a molten bath having a metal layer (as described herein) and a slag layer (as described herein) on the metal layer in a metallurgical vessel;
(b) injecting metalliferous feed material and solid carbonaceous material with a carrier gas into the molten bath via a plurality of lances/tuyeres and smelting metalliferous material to metal in the metal layer;
(c) generating an upward gas flow from the metal layer which entrains molten material that is in the metal layer and carries the molten material into the slag layer and forms a region of turbulence at least at the interface of the slag layer and the metal layer; and
(d) injecting a gas into the slag layer via a plurality of lances/tuyeres and:
(i) generating turbulence in an upper region of the slag layer; and
(ii) projecting splashes, droplets and streams of molten material from the slag layer into a top space of the vessel that is above the slag layer; and
(e) post combusting reaction gases in the top space and/or in the upper region of the slag layer.
A fundamental difference between and advantage of the process of the present invention and known non-HIsmelt direct smelting processes is that in the process of the present invention the main smelting region is the metal layer and the main oxidation (ie heat generation) region is well above the metal layer and these regions are spatially well separated and heat transfer is via physical movement and interaction of molten material between the two regions.
The process of the present invention generates two regions of turbulence, one at the metal layer/slag layer interface and the other in an upper region of the slag layer. Preferably the regions of turbulence are regions of high turbulence.